Electrical connection for waveguide or coaxial cable



A. KRAUS April 28, 1964 ELECTRICAL. CONNECTION FOR WAVEGUIDE OR COAXIAL CABLE Filed June 25.

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United States Patent 3,131,369 ELECTRHCAL CONNECTEGN FOR WAVEGUIDE GR CGAXIAL QABLE Alexander Kraus, Munich, Germany, assignor to Rohde & Schwarz, Munich, Germany, a partnership Filled June 25, 1962, Ser. No. 267,847 Claims priority, application Germany June 28, 1961 8 Claims. ((311. 333-98) Screening structures for parts carrying high frequencies are usually made up of several individual pieces. In case the operating frequency is not too high, generally, such individual pieces will consist of sheet metal. The metal pieces are connected by means of screws traversing the sheet metal. Frequently, it is necessary to make the screening parts demountable in order to have access to the interior of the screening structure.

It has been found that the screening effect of multipart screening structures is imperfect. Points of permeability are situated on the dividing lines, or gaps, of the screw mechanisms. In order to arrive at a good screening effect, the parts should be in intimate contact. This, however, could only be obtained in the immediate proximity of the pressure area. It has been found that the sheet metal between the screws buckles and an open gap will result. These connections, therefore, are really tight only at the screws where the metal sheets are pressed together with great pressure, while the gaps, even though they may be as: narrow as possible, will permit high frequency energy to escape.

Under these circumstances it is particularly diflicult to provide screening structures for Very high frequencies. In this case, instead of metal sheets, heavy plates are employed having surfaces which are polished in order to eliminate inhomogeneities. in order to obtain the desired screening effect it is necessary to press these plates together with high pressure. This is generally achieved by means of screws traversing the plates. In this case, however, it is necessary to tighten the screws under extremely high pressures. As a result, the material in proximity to the screws gives way so that surrounding surfaces, which otherwise would form cavities, will come in contact. The more surface elements attain this contact, the greater is the high frequency tightness. It is apparent that in order to obtain the necessary small deformation of a plane surface, only extremely high pressures will be effective. For these reasons the known screw connections have disadvantages if applied to very high operating frequencies.

-In other known arrangements such screening structures are made up of several telescoping coverings in cascade connection. This method is expensive and complex if applied to demountable screw fixtures.

On the other hand, it is known to tighten against high frequency the gap between two adjacent parts of a multi-element screening structure by inserting in the dividing spaces, or gaps, between the elements nettings, or otherwise perforated thin intermediate layers of conducting material, and this is done prior to the tightening of the screws of the screening elements. These intermediate layers are so constructed as to have sharp edged projections which are pressed into the material of the screening elements on numerous closely adjacent points. Thus, good contact is secured. The use of such tightening measures, however, has the great disadvantage that the tightening means does not form an element of predetermined, reproducible thickness. Depending upon the type and quality of the material, the tightening means will give more or less under the pressure of the screw fixture. As a result, the screening elements which are to be screwed together will lose their dimensions. If it were desired, for example, to apply such tighten- 3,131,369 Patented Apr. 28, 1964 ing measures to the flanges of waveguides, there would be the additional disadvantage that the tightening means could not be made accurately coinciding with the inner edge of the waveguide. The tightening means, being elastic, will.either given in the direction of the interior of the waveguide and thereby project therefrom, or it will stand back. For the electric wave, therefore, points of discontinuity will result and, in consequence, disturbing reflections. As a modification of this principle of causing sharp parts to work into a base material, it is also known to provide an arrangement in which one element of the elements to be screwed together is provided with a plane surface while its counterpart is provided with a sharp cutting edge.

If it were desired to apply this arrangement to the screw connections of waveguides, it would be necessary to arrange the cutting edge immediately on the inner edge of the waveguide. This, however, is not feasible for mechanical reasons, because, at the tightening of the screws, the cutting edge will break into the interior of the waveguide. If, however, some material is permitted to remain in the contact area at both sides of the cutting edge, the result will be a point of inhomogeneity in the waveguide, again causing reflection. Apart from that, the cutting edges can be very easily damaged and thereby made ineffective. Screening structures based on this known principle of causing sharp edges or points to penetrate into a plane base have the further disadvantage that they cannot be applied for connections which have to be frequently demounted because the plane surface will be destroyed and, as a result, the screening effect reduced.

In another known arrangement the parts to be connected are caused to penetrate each other. Practically, this should produce a large contact surface with correspondingly many contact points. In practice, thread shaped arrangements are provided whereby saw tooth protrusions of one part engage corresponding recesses of the counterpart. The parts to be connected, therefore, are not identical, but complementary. As applied to the flanges of waveguides or cables, during adjustment it will often occur that identical elements which can not be coupled with each other, will meet. Apart from that, it is impractical to provide this arrangement in rectangular shape. For this reason, this known arrangement has not succeeded in being applied practically, for example to the flanges of waveguides or cables.

It is also known to tighten plane flanges by the insertion of a soft metal foil. Metals known for this purpose, however, are not soft enough to make this. arrangement sufficiently successful.

One of the objects of the invention is to eliminate the above-mentioned defects in screening structures for very high frequencies, and in which plates are screwed together under high pressure.

A more specific object of the invention is to subdivide the engaging surfaces into a network of elemental areas .alternately protruding and recessing in space, and to arrange these elemental areas in such a way that the protruding areas of one plate are in plane contact with the protruding areas of the other plate.

I As another object of the invention, the surface of the parts screwed together is not coherent, but interrupted by plane recesses, so that contact can only occur at the protruding areas. Now if, due to limited mechanical accuracy, one of these elemental areas should protrude with respect to the general level, then it will relatively easily give under the pressure of screw tension because the material can escape into the surrounding free spaces formed by the plane recesses.

In this way, as another object of the invention, the surface realized in accordance with the invention is much the deformation of the protruding areas is elastic so that the coupling process can be repeated as often as desired without impairing the screening effect. This is indispensable, for example, on flanges of waveguides or cables used in laboratory experiments.

Another advantage of the invention consists in that there are no loose parts and that flanges made in accordance with the invention can be readily connected with flanges of usual structure. Since the protruding areas are plane, there is little possibility of damage due to scrapeoif. Accurate sizing of two parts is just as easy as with the plane surfaces used hitherto.

In one practical embodiment of the invention, a plane plate is provided, having parallel grooves machined therein, such as is made, for example, by means of a milling or planing machine. In case these grooves are arranged in one direction, the protruding areas assume the form of very small strips.

As a modification of this arrangement, other grooves are provided perpendicular to these strips resulting in gratings of protruding islets.

Frequently, it is practical to manufacture the parts in a rotation process.

In accordance with another feature of the invention, therefore, concentric grooves are made which can be readily realized on a planing machine. The protruding areas have then the shape of circular rings. In case the screening parts are cast, then it is necessary to machine only the protruding area. The recessed. areas may remain rough because they do not have any mechanical function.

More specifically, in practice, a suflicient screening effect is realized by providing a series of five to ten grooves made by milling or planing. The distance between adjacent planings or millings should be very small compared to the operating frequency For example, for very high frequencies ten grooves per five millimeters can be provided. The application of the invention, therefore, requires only little space and it is irrelevant if, due to production inaccuracies the protruding areas are not accurately lying upon each other. The screening effect will be achieved even if these individual areas are only half overlapping. In the above-mentioned example, therefore, a production accuracy of one tenth of one millimeter will be perfectly suflicient. This can be readily achieved with customary machining procedure.

In the case of coaxial cable connections, which are often to be disconnected, the connecting elements for the outer conductor are frequently in the form of so called fittings or flanges connected with the outer conductor of the cable. For coupling, the plane flange surfaces are pressed against each other. This type of connection has the particular advantage that both halves can be made geometrically identical. This is in contrast to complementary connections using plug and socket. In accordance with the invention, the screening effect is increased by providing several concentric grooves on each of the plane coupling surfaces and, in this case, the two coupling parts are still substantially identical, whereby the protruding ring areas will lie on each other in plane contact.

In addition, the recessed.

These and other objects of the invention will be more fully apparent from the drawings annexed herein in which:

FIG. 1 represents, schematically, an embodiment of the invention in cross section, as applied to the coupling of a waveguide, or the outer conductor of a coaxial transmission line.

FIGS. 2 and 3 represent corresponding side views of the two halves of the coupling shown in FIG. 1, and FIG. 4 represents, in cross section, part of the coupling surface shown in FIG. 1 at an enlarged scale.

In FIGS. 1, 2, 3, and 4, parts 1 and 2 represent two tubes of circular cross section coupled to each other. This connection can be used for the coupling of waveguides or outer conductors of coated transmission lines. The coupling is achieved by means of a threaded nut 3 which presses the front faces of tubes 1, 2 against each other, substantially along a plane schematically indicated in FIGS. 1 and 4 at 4. Both front faces of tubes 1, 2 have machined therein, as shown in FIGS. 2, 3, and 4, respectively, a number of concentric grooves 5, 6. The diameters of grooves such as shown in FIGS. 2 and 3 facing each other within the coupling plane are substantially equal.

FIGURE 4 shows, in cross section, a portion of coupling plane 4 of FIG. 1 at an enlarged scale.

The invention is not limited to the particular shapes, dimensions, or arrangements of the coupling elements shown and described, but may be applied in any appropriate form or manner whatsoever without departing from the scope of this disclosure.

I claim:

1. In a screening structure for very high frequency, a pair of coupling means including plane surfaces and means for detachably attaching said coupling means to each other along said plane surfaces; said surfaces being at least partly subdivided into networks of elemental areas alternatingly protruding and recessing and said elemental areas being so arranged that at least part of the individual protruding areas of one of saidcoupling means is in plane contact with at leastpart of the individual protruding areas of the other coupling means.

2. Structure according to claim 1 wherein the recessed areas consist of grooves formed into the corresponding plane surface.

3. Structure according to claim 2 wherein said groove has a V-shaped cross section.

4. Structure according to claim 1 wherein at least one of said coupling means is of substantially plane configuration and wherein the recessed areas consist of parallel grooves formed into the plane surface.

5. Structure according to claim 1 wherein the recessed areas consist of circular grooves formed into the plane surface.

6. Structure according to claim 1 wherein the distance between adjacent protruding areas is very small compared to the operating wave length.

7. Structure according to claim 1 comprising a coaxial cable having inner and outer conductors and wherein said coupling means are formed as flanges connected to the outer conductor; said flanges being separable under control of said attaching means.

8. Structure according to claim 1 wherein said flanges are made substantially identical in structure, at least at the portions to be connected.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A SCREENING STRUCTURE FOR VERY HIGH FREQUENCY, A PAIR OF COUPLING MEANS INCLUDING PLANE SURFACES AND MEANS FOR DETACHABLY ATTACHING SAID COUPLING MEANS TO EACH OTHER ALONG SAID PLANE SURFACES; SAID SURFACES BEING AT LEAST PARTLY SUBDIVIDED INTO NETWORKS OF ELEEMENTAL AREAS ALTERNATINGLY PROTRUDING AND RECESSING AND SAID ELEMENTAL AREAS BEING SO ARRANGED THAT AT LEAST PART OF THE INDIVIDUAL PROTRUDING AREAS OF ONE OF SAID COUPLING MEANS IS IN PLANE 